Support title tag in media oembed markup [#3574883]

Problem/motivation

The core markup for media oEmbed items omits the <title> tag from the page, resulting in an iFrame document that is an HTML page without a <title> tag.

This module can derive the title of the oembed item using the same methodology it uses for inserting the title attribute into the iframe tag itself.

Proposed new markup of media oembed template:

{% set title = resource.getTitle() ?? ("Embedded content from " ~ resource.getProvider().getName()) %}
<!DOCTYPE html>
<html>
  <title>{{ title|t }}</title>
  <head>
    <css-placeholder token="{{ placeholder_token }}">
  </head>
  <body style="margin: 0">
    {{ media|raw }}
  </body>
</html>

Issue fork iframe_title_filter-3574883

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3574883-support-title-attribute changes, plain diff MR !7
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